Patent GB-1305566-A (GB)
IPC: H04Q3/00
Filed: 1969-09-24
Abstract: 1305566 Automatic exchange systems PLESSEY CO Ltd 18 June 1970 [24 Sept 1969] 46913/69 Heading H4K In an exchange incorporating a two-stage reed relay switching network and a marker that first chooses a free interstage link and then a free outlet from the second stage switch defined by the link, the marker includes a plurality of link interrogators which are associated with those links emanating from a calling first stage switch and a so-called distributer which successively enables the interrogators until the first free link is found. A similar arrangement is used for choosing an outlet. If all the outlets from one switch are busy the link selection is recommenced. More than two stages may be utilized with obvious additions to the marker. Franking.-(Fig. 1, not shown). The network is a full availability two-stage reed relay network comprising eight 12 Î 6 matrices in the primary stage which is linked by one link per matrix to six, 8 Î 5 matrices in the secondary stage. The 96 inlets may be lines or trunks or even outlets of a previous stage while the 30 outlets may lead to registers or V.F. receivers or even to inlets of a succeeding stage. Operation.-The presence of a calling line is indicated by marking that one of leads 1DA- 8DA corresponding to the A matrix to which the line is connected. Via NAND gate G1 a so called distributer DCA is caused to mark that one of its outlets TA1-TA6 which immediately follows the outlet last marked during a preceding link selecting operation. After about 4 msecs. of a lead, e.g. IDA being marked, the corressponding link access relay 1A comes up to connect the hold wires H, of each of the links emanating from the calling matrix, to the coincidence gate selector G3-G8. If outlet TA1 is marked say, and if the first link is free, as denoted by positive potential via RL1, then gate G3 opens to prepare a link marking relay 1MA and via gates G15, G16, G2 the distributer is caused to maintain the marking on outlet TA1. If the first link is not free, as denoted by earth on the H wire, the logic conditions transmitted by gates G15, G16 are such as to open gate G2 in coincidence with a signal from delay circuit DELA whereby DCA is stepped-on to mark its next outlet-in this case TA2. The procedure repeats until a free link is found or until a predetermined period expires whereupon the start marking on lead IDA is removed and another caller is given access to the marker. Assuming that the first link is free, then outlet access relay 1B, corresponding to the B switch accessible via first AB links, is marked via G3 and inverter IV19 and, in addition, via gate G35, distributer DCB is caused to mark one of its outlets, say TB1. After 4 msecs. 1B comes up to connect the H leads of the outlets to coincidence gate selector G25-G29. Again, if the first outlet is free gate G25 prepares an outlet marking relay 1MB and locks DCB whereas if it is busy DCB is stepped-on, when the delayed signal via DELB appears, until a free outlet is found. In this case, recycling over the outlets will not occur since if all outlets are busy gate G30 immediately causes the link distributer DCA to be stepped-on so as to test for a free link to another B switch. Eventually, therefore, gates G31 and G34 should be primed such as to allow relay SM to operate. This enables the prepared link (1MA) and outlet (1MB) marking relays and applies positive potential V1 via its contact SM3 and the calling line marking contact IMC to the inlet H wire. The chosen A crosspoint switches through to this potential and the negative potential V2 supplied via contact 1MA1 and diode MDA. Thereafter the B crosspoint switches through and the connection holds to - ve battery V4 in the register. The busy condition on the link and outlet causes gates G3 and G25 to close thus dropping relays 1MA and 1MB, but the two distributers do not step because of the earth supplied via SM4. Shortly afterwards, the start marking is removed from 1DA so that 1A and thus SM fall back to release the marker. The distributers step-on one position, i.e. to TA2 and TB2 in this example, so as to equalize traffic over the network.